WASHINGTON — CIA Director Mike Pompeo scrapped his appearance Thursday at Harvard University over the school's decision to make Chelsea Manning, who was convicted of leaking classified information, a visiting fellow.

Pompeo called Manning an "American traitor." He said he agreed with military and intelligence officials who believe Manning's leak endangered the lives of CIA personnel.

Pompeo was scheduled to appear at Harvard's Kennedy School of Government to discuss allegations of Russian involvement in last year's presidential election, the nuclear standoff with North Korea and other global security concerns.

Minutes after the event was to begin, Douglas Elmendorf, dean of the John F. Kennedy School of Government, took the stage and told the audience Pompeo was not there and would not speak.

"We will try to reschedule it as soon as we can, but the CIA director, is obviously, in charge of his schedule," Elmendorf said. "We are not in charge of his schedule and he gets to decide when and where he speaks, of course."

Several hours later, the CIA released a letter that Pompeo wrote to a Harvard official.

Pompeo, who has a law degree from Harvard, said he didn't make the decision lightly. He wrote that he would betray the trust of CIA employees if he appeared.

Manning was released from a military prison in Fort Leavenworth, Kansas, on May 17 after serving seven years of a 35-year sentence, which was commuted by former President Barack Obama in his final days in office. Obama said in January he felt justice had been served.

Manning, a 29-year-old transgender woman, formerly known as Bradley Manning, told ABC's "Good Morning America" in a recent interview that she was prompted to give the 700,000 military and State Department documents to WikiLeaks because of the human toll of the "death, destruction and mayhem" she saw as an Army intelligence analyst in Iraq.

In his letter, Pompeo reiterated his earlier claim that WikiLeaks is a U.S. adversary "akin to a hostile foreign intelligence service." He stressed that his decision had nothing to do with Manning's transgender identity.

"It has everything to do with her identity as a traitor to the United States of America and my loyalty to the officers of the CIA," Pompeo said.

"Harvard's actions implicitly tell its students that you too can be a fellow at Harvard and a felon under United States law," he wrote.

Earlier in the day, Mike Morell, former deputy director and acting director of the CIA, sent a resignation letter to Elmendorf. Morell told Elmendorf he was resigning immediately over the school's decision to invite Manning to be a visiting fellow at the Kennedy School's Institute of Politics.

Morell said he could not be part of an organization that "honors a convicted felon and leaker of classified information." Pompeo said Morell's exit was "Harvard's loss."

Harvard also has invited former White House press secretary Sean Spicer, former Trump campaign manager Corey Lewandowski and MSNBC hosts Joe Scarborough and Mika Brzezinski. Harvard says Manning will be among fellows who will visit the campus for a "limited" number of events meant to spark campus discussion.